As is known in the art, aircraft file flight plans with an air traffic control (ATC) system prior to take off. This is mandatory if the flight is operating under Instrument Flight Rules (IFR) and optional if operating under Visual Flight Rules (VFR). A beacon code is assigned to the aircraft by the ATC system to enable the ATC system to track the aircraft during a flight. This, code, which is stored in a transponder on the aircraft, links a track and a flight plan to enable air traffic control to identify a target in an airspace. Typically, a beacon code is given to the flight crew by clearance delivery for a flight conducted under IFR as part of the clearance process. The clearance may also be given to the flight crew by the tower during the hold for the departing runway. Once issued, the beacon code stays with the aircraft through the entire route. However, there are cases where the beacon code is re-assigned, such as when a flight passes from one air traffic center to another. For flights operating under VFR the standard beacon code in the United States is 1200. If the flight crew of the VFR flight requires ATC assistance, they typically request flight following (or Flight Information Service in the United Kingdom) in which case the controller allocates to the flight a specific beacon code which should stay with the flight throughout the route. This may not be the case as the flight transitions through several centers and each center may allocate a different beacon code to the flight.
An unnecessary by-product of flight crew changing beacon codes is that the transponder may cycle through an emergency code inadvertently (i.e. 7500, 7600 or 7700). This invariably causes nuisance alerts on the ATC system controlling the flight. This problem occurs most often on older transponders that have rotary dial modulation of the individual digits that comprise the beacon code.
Newer transponder equipment is digital so that the flight crew types in the numbers for the code which eliminates the cycling through emergency codes inadvertently. However, there is still controller flight crew voice chatter required, On occasion, the flight crew may read back the wrong beacon code verbally provided by air traffic control, especially between a flight crew and controllers in situations where language is an issue. Further conversation is then required to correct the misinformation all of which distracts the flight crew and/or controllers from other tasks.